(1) Field of the Invention
The present invention relates to a ball grid array package which is contained on a mother-board of a portable electronic device.
(2) Description of the Related Art
Portable electronic devices use semiconductor chip packages which are contained on a motherboard. There are various types of packages, such as pin-grid-array packages, gull-wing lead packages and ball-grid-array packages. Recently, there is an increasing demand to make the portable electronic devices as small as possible in size. In conformity with the demand, it is needed to increase the package density and make the motherboard smaller in size.
The ball-grid-array packages are useful and advantageous to increase the package density and make the motherboard size smaller.
FIGS. 1A, 1B and 1C show a conventional ball-grid-array (BGA) package 10. FIG. 1A is a side view of the conventional BGA package 10. FIG. 1B is a perspective view of the bottom of the conventional BGA package 10. FIG. 1C is an enlarged side view of a portion 11 of the conventional BGA package 10.
As shown in FIGS. 1A and 1B, the conventional BGA package 10 comprises a package board 12, a semiconductor chip 13 contained on the package board 12, a resin material 14 encapsulating the semiconductor chip 13, and a plurality of solder balls 15 arrayed in a grid formation on the bottom of the package board 12.
As shown in FIG. 1C, the package board 12 has a bottom surface, a top surface and an internal portion between the bottom surface and the top surface. Solder ball pads 16 are formed on the bottom surface of the package board 12, and wire bonding pads 17 are formed on the top surface thereof. In the internal portion of the package board 12, wiring patterns 18 and vias 19 are formed. The solder ball pads 16 and the wire bonding pads 17 are electrically connected by the wiring patterns 18 and the vias 19.
As shown in FIG. 1C, a wire 20 is bonded at one end to the semiconductor chip 13 and at the other end to one of the wire bonding pads 17 on the top of the package board 12. The solder balls 15 are soldered to the solder ball pads 16 on the bottom of the package board 12, and secured to the BGA package 10. The periphery of each of the solder ball pads 16 is encircled by a solder resist 22.
As shown in FIGS. 1A and 1C, the solder balls 15 are soldered to pads 26 of a motherboard 25 (indicated by two-dot chain lines in FIGS. 1A and 1C) so that the conventional BGA package 10 is housed in the motherboard 25. The soldering of the solder balls 15 and the pads 26 is carried out by passing the motherboard 25 with the conventional BGA package 10 temporarily bonded thereto through a reflow soldering furnace.
As indicated by two-dot chain lines in FIG. 1C, a wiring pattern 27 extends from one of the pads 26 on the motherboard 25, and a chip element pad 28 is formed on the motherboard 25 at one end of the wiring pattern 27. A semiconductor chip element 29 is soldered to the chip element pad 28. A combination of the motherboard 25, the conventional BGA package 10 and the semiconductor chip element 29 contained on the motherboard 25 is called a multichip module 30. The multichip module 30 is incorporated in a portable electronic device.
In the multichip module 30, the locations at which the solder balls 15 on the bottom of the BGA package 10 are actually soldered to the pads 26 on the top of the motherboard 25 are concealed by the BGA package 10. For this reason, the multichip module 30 has the following problems:
(1) A defective soldering of the solder balls 15 and the pads 26 cannot be easily repaired by using a soldering iron. If a defective soldering of the solder balls 15 and the pads 26 is found, an effective repairing measure is not taken and the multichip module 30 has to be a defective part. PA1 (2) It is difficult to perform a modification of the electrical characteristics of the multichip module 30 (or the BGA package 10) by soldering of a jumper wire or a circuit element. There is no space in the multichip module 30 (or the BGA package 10) adequate for the soldering of the jumper wire or the circuit element. PA1 (3) It is difficult to perform a testing of the condition of the soldered connections between the solder balls 15 and the pads 26. There is no space in the multichip module 30 (or the BGA package 10) adequate for contacting a probe of a tester. Therefore, it is difficult to assure the reliability of the soldered connections between the solder balls 15 and the pads 26 in the multichip module 30.